The present invention relates to a valve actuating method for opening and closing intake valves and exhaust valves in internal combustion engines while suspending the operation of the some of these valves to keep them in the closing positions in response to the state of operation of the engine.
Hitherto, such an internal combustion engine has been known as having at least three valves including intake and exhaust valves on each cylinder, wherein all of the three valves are actuated in high-speed operation of the engine to increase the output power from the engine, while, in the low or medium operation of the engine, a part of the intake or the exhaust valves are held in the closed state and made to suspend the operation to increase the output power in the low and medium speed regions.
This type of engine incorporates a valve actuating mechanism having a valve operation suspending function for suspending at least one of the intake and exhaust valves. FIG. 1 shows such a valve actuating mechanism having a valve operation suspending function, incorporating a hydraulic lifter as a retaining means. In FIG. 1, a reference numeral 1 denotes a cam, 2 denotes an intake valve or an exhaust valve, 3 denotes a rocker arm, and 4 denotes a hydraulic lifter i.e. the retaining means supporting the fulcrum of the rocker arm. The hydraulic lifter 4 includes a hollow plunger, i.e. a supporting member, which engages at its upper end with the fulcrum of the rocker arm 3, a casing 8 slidably accomodating the plunger 5 with a high-pressure chamber 6 defined at the lower side of the plunger 5 and provided at the lower end thereof with an oil discharge port 7 for discharging oil from the high-pressure chamber 6, a check valve 9 disposed in an opening between the hollow 5a in the plunger 5 and the high-pressure chamber 6 and adapted for preventing pressurized oil from flowing back into the hollow 5a from the high-pressure chamber 6, and oil supply passages 10a and 10b for supplying the hollow portion 5a of the plunger 5 with oil. The check valve 9 has a ball valve 11 biased by a spring 13 in a retainer 12 and seated on a valve seat formed around the opening. A spring 14 for upwardly biasing the plunger 5 is disposed in the high-pressure chamber 6.
A discharge limiting valve 15 is adapted to limit the discharge of the oil from the oil discharge port 7. The discharge limiting valve, accomodated by the casing 8, has a valve seat formed in a passage 16 leading to the outside of the casing 8, a ball valve 17 biased by a spring 19 in a retainer 18 so as to be seated on the valve seat, and a push rod 21 driven by a solenoid 20 to push the ball valve 17. A reference numeral 22 denotes an intake or exhaust manifold, 23 denotes a valve guide an 24,25 denote valve springs.
In the normal operation of this valve actuating mechanism, the rocker arm 3 makes a rocking motion around the fulcrum supported by the plunger 5 of the hydraulic lifter 4 to open and close the valve 2 in each rotation of the cam 1. The hydraulic lifter 4 can maintain the clearance in the valve actuating mechanism zero to afford a silent and maintenance-free operation. As the solenoid 20 is energized as necessitated, the push rod 21 is moved to the left as viewed in the drawings to push the ball valve 17 so that the passage 16 is opened to relieve the oil from the high-pressure chamber 6 so that the plunger 5 supporting the fulcrum of the rocker arm 3 is lowered when the cam 1 takes the lifting position, because the force of the spring 14 for upwardly biasing the plunger 5 is smaller than the force of the valve springs 24,25. Therefore, the rotation of the cam 1 causes only up and downward movement of the rocker arm 3 so that the valve 2 is held in the closed position to suspend its operation.
With the conventional valve actuating mechanism explained above, it is possible to increase the output power of the engine in the low and medium speed range of the engine operation by suspending the operation of a part of the valves. The plunger 5 in the hydraulic lifter 4, however, makes an up and downward reciprocal motion by the action of the rocker arm 3 and the spring 14 following up the operation of the cam 1 even during the suspension of operation of the valve. Thus, the engine is obliged to make a wasteful work for driving the plunger 5 uselessly overcoming to force of the spring 14. In addition, during the reciprocal motion of the plunger 5 mentioned above, the oil is made to flow into and out of the high-pressure chamber 6 through the passage 16 in the discharge limiting valve 15. This state tends to cause a generation of the bubbles in the oil due to a phenomenon called cavitation. If there is any bubble remaining in the high-pressure chamber 6, the hydraulic lifter 4 cannot perform its function to make the fulcrum 3 of the rocker arm 3 rigid. Furthermore, the bubbles produced by the cavitation contain an ozonic air which tends to promote the corosion of mechanical parts.